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Make CPU utilization checks in the thread pool configurable #112789

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Feb 25, 2025
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Make CPU utilization checks in the thread pool configurable #112789

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31 changes: 28 additions & 3 deletions src/libraries/System.Private.CoreLib/src/System/Threading/PortableThreadPool.GateThread.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -27,10 +27,26 @@ private static void GateThreadStart()
bool debuggerBreakOnWorkStarvation =
AppContextConfigHelper.GetBooleanComPlusOrDotNetConfig("System.Threading.ThreadPool.DebugBreakOnWorkerStarvation", "ThreadPool_DebugBreakOnWorkerStarvation", false);

// CPU utilization is updated when the gate thread performs periodic activities (GateActivitiesPeriodMs), so
// that would also affect the actual interval. Set to 0 to disable using CPU utilization and have components
// behave as though CPU utilization is low. The default value of 1 causes CPU utilization to be updated whenever
// the gate thread performs periodic activities.
int cpuUtilizationIntervalMs =
AppContextConfigHelper.GetInt32Config(
"System.Threading.ThreadPool.CpuUtilizationIntervalMs",
"DOTNET_ThreadPool_CpuUtilizationIntervalMs",
defaultValue: 1,
allowNegative: false);

// The first reading is over a time range other than what we are focusing on, so we do not use the read other
// than to send it to any runtime-specific implementation that may also use the CPU utilization.
CpuUtilizationReader cpuUtilizationReader = default;
_ = cpuUtilizationReader.CurrentUtilization;
int lastCpuUtilizationRefreshTimeMs = 0;
if (cpuUtilizationIntervalMs > 0)
{
lastCpuUtilizationRefreshTimeMs = Environment.TickCount;
_ = cpuUtilizationReader.CurrentUtilization;
}

PortableThreadPool threadPoolInstance = ThreadPoolInstance;
LowLevelLock threadAdjustmentLock = threadPoolInstance._threadAdjustmentLock;
Expand Down Expand Up @@ -102,8 +118,17 @@ private static void GateThreadStart()
(uint)threadPoolInstance.GetAndResetHighWatermarkCountOfThreadsProcessingUserCallbacks());
}

int cpuUtilization = (int)cpuUtilizationReader.CurrentUtilization;
threadPoolInstance._cpuUtilization = cpuUtilization;
// Determine whether CPU utilization should be updated. CPU utilization is only used by the starvation
// heuristic and hill climbing, and neither of those are active when there is a pending blocking
// adjustment.
if (cpuUtilizationIntervalMs > 0 &&
threadPoolInstance._pendingBlockingAdjustment == PendingBlockingAdjustment.None &&
(uint)(currentTimeMs - lastCpuUtilizationRefreshTimeMs) >= (uint)cpuUtilizationIntervalMs)
{
lastCpuUtilizationRefreshTimeMs = currentTimeMs;
int cpuUtilization = (int)cpuUtilizationReader.CurrentUtilization;
threadPoolInstance._cpuUtilization = cpuUtilization;
}

if (!disableStarvationDetection &&
threadPoolInstance._pendingBlockingAdjustment == PendingBlockingAdjustment.None &&
Expand Down
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